Central nervous system infections can be divided into several categories that usually can be readily distinguished from each other by cerebrospinal fluid examination as the first step toward etiologic diagnosis (Table 30–1) (eFigure 30–2).
Table 30–1.Typical cerebrospinal fluid findings in various central nervous system diseases. ||Download (.pdf) Table 30–1. Typical cerebrospinal fluid findings in various central nervous system diseases.
|Diagnosis ||Cells/mcL ||Glucose (mg/dL) ||Protein (mg/dL) ||Opening Pressure |
|Normal ||0–5 lymphocytes ||45–851 ||15–45 ||70–180 mm H2O |
|Purulent meningitis (bacterial)2 community-acquired ||200–20,000 polymorphonuclear neutrophils ||Low (< 45) ||High (> 50) ||Markedly elevated |
|Granulomatous meningitis (mycobacterial, fungal)3 ||100–1000, mostly lymphocytes3 ||Low (< 45) ||High (> 50) ||Moderately elevated |
|Spirochetal meningitis ||100–1000, mostly lymphocytes3 ||Normal ||High (> 50) ||Normal to slightly elevated |
|Aseptic meningitis, viral meningitis, or meningoencephalitis4 ||25–2000, mostly lymphocytes3 ||Normal or low ||High (> 50) ||Slightly elevated |
|“Neighborhood reaction”5 ||Variably increased ||Normal ||Normal or high ||Variable |
Collection of cerebrospinal fluid. (Reproduced, with permission, from Chesnutt MS et al. Office & Bedside Procedures. Copyright © 1992 by The McGraw-Hill Companies, Inc.)
Patients with bacterial meningitis usually seek medical attention within hours or 1–2 days after onset of symptoms. The organisms responsible depend primarily on the age of the patient as summarized in Table 30–2. The diagnosis is usually based on the Gram-stained smear (positive in 60–90%) or culture (positive in over 90%) of the cerebrospinal fluid.
Table 30–2.Initial antimicrobial therapy for purulent meningitis of unknown cause. ||Download (.pdf) Table 30–2. Initial antimicrobial therapy for purulent meningitis of unknown cause.
|Population ||Usual Microorganisms ||Standard Therapy |
|18–50 years ||Streptococcus pneumoniae, Neisseria meningitidis ||Vancomycin1 plus ceftriaxone2 |
|Over 50 years ||S pneumoniae, N meningitidis, Listeria monocytogenes, gram-negative bacilli, group B streptococcus ||Vancomycin1 plus ampicillin,3 plus ceftriaxone2 |
|Impaired cellular immunity ||L monocytogenes, gram-negative bacilli, S pneumoniae ||Vancomycin1 plus ampicillin3 plus cefepime4 |
|Postsurgical or posttraumatic ||Staphylococcus aureus, S pneumoniae, aerobic gram-negative bacilli, coagulase-negative staphylococci,5 diphtheroids (eg, Propionibacterium acnes)5 (uncommon) ||Vancomycin1 plus cefepime4 |
The presentation of chronic meningitis is less acute than purulent meningitis. Patients with chronic meningitis usually have a history of symptoms lasting weeks to months. The most common pathogens are Mycobacterium tuberculosis, atypical mycobacteria, fungi (Cryptococcus, Coccidioides, Histoplasma), and spirochetes (Treponema pallidum and Borrelia burgdorferi). The diagnosis is made by culture or in some cases by serologic tests (cryptococcosis, coccidioidomycosis, syphilis, Lyme disease).
Aseptic meningitis—a much more benign and self-limited syndrome than purulent meningitis—is caused principally by viruses, especially herpes simplex virus and the enterovirus group (including coxsackieviruses and echoviruses). Infectious mononucleosis may be accompanied by aseptic meningitis. Leptospiral infection is also usually placed in the aseptic group because of the lymphocytic cellular response and its relatively benign course. This type of meningitis also occurs during secondary syphilis and disseminated Lyme disease. Prior to the routine administration of measles-mumps-rubella (MMR) vaccines, mumps was the most common cause of viral meningitis. Drug-induced aseptic meningitis has been reported with nonsteroidal anti-inflammatory drugs, sulfonamides, and certain monoclonal antibodies.
Encephalitis (due to herpesviruses, arboviruses, rabies virus, flaviviruses [West Nile encephalitis, Japanese encephalitis], and many others) produces disturbances of the sensorium, seizures, and many other manifestations. Patients are more ill than those with aseptic meningitis. Cerebrospinal fluid may be entirely normal or may show some lymphocytes and, in some instances, (eg, herpes simplex) red cells as well. Influenza has been associated with encephalitis, but the relationship is not clear. An autoimmune form of encephalitis associated with N-methyl-D-aspartate receptor antibodies should be suspected in younger patients with encephalitis and associated seizures, movement disorders, and psychosis.
E. Partially Treated Bacterial Meningitis
Previous effective antibiotic therapy given for 12–24 hours will decrease the rate of positive cerebrospinal fluid Gram stain results by 20% and culture by 30–40% but will have little effect on cell count, protein, or glucose. Occasionally, previous antibiotic therapy will change a predominantly polymorphonuclear response to a lymphocytic pleocytosis, and some of the cerebrospinal fluid findings may be similar to those seen in aseptic meningitis.
As noted in Table 30–1, this term denotes a purulent infectious process in close proximity to the central nervous system that spills some of the products of the inflammatory process—white blood cells or protein—into the cerebrospinal fluid. Such an infection might be a brain abscess, osteomyelitis of the vertebrae, epidural abscess, subdural empyema, or bacterial sinusitis or mastoiditis.
G. Noninfectious Meningeal Irritation
Carcinomatous meningitis, sarcoidosis, systemic lupus erythematosus, chemical meningitis, and certain medications—nonsteroidal anti-inflammatory drugs, OKT3, TMP-SMZ, and others—can also produce symptoms and signs of meningeal irritation with associated cerebrospinal fluid pleocytosis, increased protein, and low or normal glucose. Meningismus with normal cerebrospinal fluid findings occurs in the presence of other infections such as pneumonia and shigellosis.
Brain abscess presents as a space-occupying lesion; symptoms may include vomiting, fever, change of mental status, or focal neurologic manifestations. When brain abscess is suspected, a CT scan should be performed. If positive, lumbar puncture should not be performed since results rarely provide clinically useful information and herniation can occur. The bacteriology of brain abscess is usually polymicrobial and includes S aureus, gram-negative bacilli, streptococci, and mouth anaerobes (including anaerobic streptococci and Prevotella species).
I. Health Care–Associated Meningitis
This infection may arise as a result of invasive neurosurgical procedures (eg, craniotomy, internal or external ventricular catheters, external lumbar catheters), complicated head trauma, or hospital-acquired bloodstream infections. Outbreaks have been associated with contaminated epidural or paraspinal corticosteroid injections. In general, the microbiology is distinct from community-acquired meningitis, with gram-negative organisms (eg, Pseudomonas), S aureus, and coagulase-negative staphylococci and, in the outbreaks associated with contaminated corticosteroids, mold and fungi (Exserohilum rostratum and Aspergillus fumigatus) playing a larger role.